Cablevision Chief Operating Officer James Dolan said the spin-off would allow its investors "to more clearly evaluate each of the separate companies' assets and future potential." Cablevision, which is based in Bethpage, N.Y., owns cable systems reaching more than 3 million homes, mostly in the New York City region.

Besides its systems, Cablevision will also continue to operate the newspaper New York Newsday, the MSG Varsity,a high school sports channel and Clearview Cinemas.

-- Joe Flint

For the record: This post was updated to note that the MSG channel that will remain with Cablevision is MSG Variety, not the MSG Networks, which are part of Madison Square Garden.